In the field of color printing, it is desirable to achieve as large of a color gamut as possible without sacrificing necessary ink performance parameters. It is also desirable to achieve secondary colors from the primaries which the consumer readily associates with a name such as blue or red. When the color ink is used in a digital printing device, that is, one in which a dot of color is either present or absent, the ability of the primaries to give recognizable secondaries is even more important. In printing processes such as lithography, dye transfer, and some types of thermal transfer, it is possible to vary spot size so that less is demanded of the primary colored inks when producing a good secondary.
If such an ink is to be used in an ink-jet printing device, characteristics such as crusting, long term stability, and materials compatibility must also be addressed. If the ink is to be used in a thermal ink-jet printer, the further constraint of being thermally stable (kogation-resistant) is added.
In general, a successful ink set for color ink-jet printing must have the following properties: good crusting resistance, good stability, the proper viscosity, the proper surface tension, recognizable secondaries, high color saturation, little color-to-color bleed, rapid drytime, no negative reaction with the vehicle, be highly soluble in the vehicle, consumer-safe, and low strike-through. While formation of colors on plain papers is required, it is also necessary that the ink set be useful on other print media as well, such as on transparency media. When placed into a thermal ink-jet system, the ink set must also be kogation-resistant.
Some of the conditions may be met by vehicle design; other conditions must be met by the proper selection and combination of the dyes.
While it is fairly simple and obvious to make one ink which will satisfy the above conditions, it becomes very difficult to produce a set of inks to be used together to give three acceptable primaries and which will satisfy these conditions. Indeed, the color and overall appearance of hard copy output are critical to its ultimate acceptability and, thus, saleability in the marketplace.